Administering an injection is a process which presents a number of risks and challenges for users and healthcare professionals, both mental and physical.
Injection devices (i.e. devices capable of delivering medicaments from a medication container) typically fall into two categories—manual devices and auto-injectors.
In a manual device—the user must provide the mechanical energy to drive the fluid through the needle. This is typically done by some form of button/plunger that has to be continuously pressed by the user during the injection. There are numerous disadvantages to the user from this approach. If the user stops pressing the button/plunger then the injection will also stop. This means that the user can deliver an underdose if the device is not used properly (i.e. the plunger is not fully pressed to its end position). Injection forces may be too high for the user, in particular if the patient is elderly or has dexterity problems.
The extension of the button/plunger may be too great. Thus it can be inconvenient for the user to reach a fully extended button. The combination of injection force and button extension can cause trembling/shaking of the hand which in turn increases discomfort as the inserted needle moves.
Auto-injector devices aim to make self-administration of injected therapies easier for patients. Current therapies delivered by means of self-administered injections include drugs for diabetes (both insulin and newer GLP-1 class drugs), migraine, hormone therapies, anticoagulants etc.
Auto-injectors are devices which completely or partially replace activities involved in parenteral drug delivery from standard syringes. These activities may include removal of a protective syringe cap, insertion of a needle into a patient's skin, injection of the medicament, removal of the needle, shielding of the needle and preventing reuse of the device. This overcomes many of the disadvantages of manual devices. Injection forces/button extension, hand-shaking and the likelihood of delivering an incomplete dose are reduced. Triggering may be performed by numerous means, for example a trigger button or the action of the needle reaching its injection depth. In some devices the energy to deliver the fluid is provided by a spring. In other devices this is achieved by an electromechanical drive. Devices with electromechanical and/or electronic components may comprise a drive for electrically displacing a bung within the cartridge or syringe.
WO 02/083209 A1 discloses a pump system for an infusion system including a linear drive which minimizes the space occupied by the pump system in a portable housing. A motor and a motor drive shaft are arranged in parallel with, and adjacent to a syringe and lead screw. A gear box connects the drive shaft and lead screw to transfer rotational movements between them. A piston driving member, such as a cone or drive nut converts the rotational movement of the lead screw into linear motion of a syringe piston. Sensors detect when the piston or cone is in a “home” position and in an “end” position, respectively. A clamping member selectively clamps the lead screw against linear motion in at least a dispensing direction. Optionally, a proximity sensor is used to ensure that the cone and the piston are abutting during dispensing.